text:
Are the advantages of a coaxial rotor on a helicopter also applicable to a ducted fan?
A coaxial rotor helicopter is connected to the same engine and has the advantage of anti-torque and a +/- 25% increase in lift.
My question is if a coaxial ducted fan connected to the same engine would also have a +/- 25% increase in forward motion ?

Part of the gain of coaxial rotors on a helicopter is not having to power the tail rotor (IIRC it takes ~10%). So for contra-rotating propellers and fans, which don't need a tail rotor, the advantage is smaller, about 6–16% [1].
Now ducted fans (assuming as used in turbofan engines) usually contain stators. These do not stop the rotation of the flow (that takes away the energy) completely, but they do reduce it significantly and with much lower complexity. The remaining possible gain would probably be at most couple of percent and that is likely not worth the increased complexity and weight of additional gears. Don't forget that turbofans run at significantly higher rotation speeds than propellers.

@KorvinStarmast, I am not. I am comparing contra-rotating rotors and contra-rotating propellers.

@KorvinStarmast, the question is about whether the advantage contra-rotating rotors (on helicopters) have applies to fans (in airplane turbofan engines). So I am first saying what that advantage is, and then that it does not apply to propellers and fans.

@KorvinStarmast, because propellers are between rotors and fans.


text:
Can small airplanes be towed (or carried) as cargo to be dropped at some other location by air?
Is there any present technology where a large plane can carry a small plane (or multiple small planes) and drop it midair where the small plane deploys itself? This would be very good from defense point of view, where small fighter jets with limited range could be dropped off by large airplanes with very long range.

Related answer: Can a fighter jet land on a modified airliner

This might be worth reading: https://en.wikipedia.org/wiki/Parasite_aircraft

If you are talking about externally carrying/deploying other aircraft, this has already been done with the B-52 (albeit for testing purposes) carrying the X-15.
I'm not too sure about having an aircraft drop out of a cargo bay such as the C-130.
On a side note military gliders were used extensively during WW2 and some were capable of carrying light tanks. The gliders were usually towed behind larger bombers to give them the required altitude and speed. They were used because of their wooden construction allowing a stealthy approach due to the reduced radar signature.

I doubt stealth was the reason. Many gliders were used only once. Wood is light and cheap. Steel would be heavy and aluminum to expensive.

Both steel and aluminum were also "strategic materials" required for the production of other essential materiel (tanks, ships, guns, field equipment, powered aircraft). The gliders were used primarily because they could get heavier equipment like jeeps and artillery into the field, and also because the ability to glide meant that the C-47 tow craft didn't have to overfly German territory (or at least not as deeply), which protected the more valuable powered planes. Bombers were rarely used as tugs for many reasons, primarily that they were way too valuable for actually delivering ordinance.

Stealth was a benefit of gliders but mainly because of their silence at low level approaching the target. Other reasons to use them included: they only needed to be able ditch  safely on rough ground without a care for taking off again (over powered transports landing); were able to offload a unit ready to fight (over powered transports dropping paratroopers); required less training of both pilots and passengers (over paratroopers).

Wood was a surprisingly good material for aircraft bodies and wings. Just reference the de Havilland Mosquito fighter bomber, aka the Wooden Wonder,which was surprisingly robust, perhaps more so than similar metal aircraft.Aircrew particularly enjoyed it because opposing machine gun fire went straight through rather than rattling around inside as shrapnel, significantly reducing casualties. Link: https://en.wikipedia.org/wiki/De_Havilland_Mosquito

Stealth technology was not really a subject in WW2 (the Ho-229 being the sole noteable exception). The use of gliders required air superiority (Germany on the Eastern Front, Allies over Normandy), and the very limited range would put the tow craft on the radar anyway. The "antidote" for radar at the time was chaff or active jamming, not avoidance. Gliders were build of (cheap) wood because they were strictly one-way craft.

Parasite aircraft is a concept that has been considered.
During the era of the zeppelins several countries experimented with launching fighter aircraft from airships, mainly as a way to get the fighter crafts to a relevant altitude while conserving fuel.  However none of these projects where realized before the end of WWI.
During WWII soviet used Tupolev TB-3's to carry I-16 dive bombers, a culmination of experiments started during the 1930's. Some of Japan's kamikaze crafts where also launched as parasite aircraft.
In an escort role Germany experimented with parasite craft solutions as a way to bypass the very short operational range of rocket powered fighters, but these experiments where ultimately judged unsuitable.
The extreme range of US strategic bombers in late WWII and early cold war lead US to consider parasite fighters as an escort solution.  However these attempts where eventually scrapped in favour of aerial refueling, as this was considered a safer option.
Source: https://en.wikipedia.org/wiki/Parasite_aircraft

Welcome to Aviation SE, Taemyr. Could you please add the gist of the link directly. If links go stale, your answer would lose most of its value as it is.

@PeterKämpf Attempted to include the gist of the article.

It's worth noting that, today, the escort fighter is obsolete. Today, we use cruise missiles, fighter-bombers and/or stealth, depending on the circumstances. A bomber that would require escort in a defenced airspace, such as a B-52, is only used once air superiority is achieved so no escort is needed.

@Vladimir At least in US practice, there are no nuclear bombs dropped by non-stealth bombers. US B-52s just use cruise missiles; bombs are only used on fighter-bombers and B-2s.

@VladimirF The nuclear bomber is largely obsolete; it's vulnerable on the ground and hard to get to the target. The retaliatory strike comes from submarines.

small fighter jets with limited range could be dropped off by large airplanes with very long range

That sounds like a one-way mission.
Some Zeppelins and some US Navy airships did carry small aircraft that could be both launched and, importantly from the pilot's perspective, recovered in mid-air.
However in the modern world, the approach you describe is not used.
If fighters are needed beyond normal operational range of their bases, air forces will either use in-flight refuelling or create a forward operating base nearer the mission target. Aircraft carriers are a popular solution to this requirement, if adequate time is available.

+1 for mentioning that it's usually desired to get the fighters back home at some point.

Since your question is about the tech, it very much does exist in a few forms at least for aircraft of varying size.
The Bell X-1 (the plane that broke the sound barrier) was a mid flight deploy from a B-29. This was a result of its low fuel load it could not really get its self off the ground and then have enough fuel to break the sound barrier.

This became common for a lot of the high speed test crafts developed over the years. Up through the X-15 (the fastest thing out there)

The first space shuttle tests were done by flying the shuttle to altitude on a modified 747 and deploying it for an unpowered decent so the tech is there even for large craft.

The more modern Space Ship One also uses this configuration to get it to altitude easier.

The tech is there and has been used over the years. Now to the more realistic question "would you do it" most likely no. As you mentioned there is a case for small limited range planes being deployed at distance but the simpler solution to that is a mid-air refuel. This accomplishes the range extension and allows the plane to get back home. The other option is a drop tank which also extends the range of a plane.
Note: Another kinda of cool solution to the problem was to weld 2 planes into one like the North American F-82 Twin Mustang.

Also, it's not unknown to tow a sailplane from one airport to within gliding distance of another.

Germany had some (very) limited success in WWII with the Mistel concept, which is basically the opposite of what you mentioned:
The smaller of two craft was the piloted one, the bigger craft being an explosive-carrying drone -- like a really big glide bomb. The most common combination was a Fw-190 figher/bomber carrying a Ju-88 drone.

This would be very good from defense point of view, where small fighter jets with limited range could be dropped off by large airplanes with very long range.

Parasite aircraft as a way of increasing the range of fighters has been tried repeatedly, with everything from airships to heavy bombers as the mothership.  It turns out to be much harder than it sounds, and has generally been abandoned in favor of dedicated tankers and mid-air refueling.

where a large plane can carry a small plane (or multiple small planes) and drop it midair where the small plane deploys itself

In addition to those concepts, let us not forget the Goodyear Inflatoplane, which was designed specifically to be dropped from aircraft, inflated, and flown away.
Designed for pilot rescue, the idea of dropping an aircraft in and flying it out was revealed to be ultimately impossible when one considers pilots in a Vietnam jungle.

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text:
Can a FAA "Letter of Authorization" be used when there are no pilots that are current on a type rating?
A pilot has multiple type ratings and wants to train for another aircraft (e.g. DC-4) which is on his Part 125 certificate. Unfortunately, there are no available pilots with currency on this aircraft type, but some do have the rating.
Can the FAA authorize a "Letter of Authorization" for the pilot to train based on his other type ratings? Or, could the FAA issue a letter of authorization to a pilot with the appropriate type rating to be used as a training instructor?
As of today the FAA has a few examiners who can issue the type rating for this aircraft, but have lapsed the currency requirement. Therefore, the question is one of training and how to obtain it; not the actual addition of the rating which they can provide.

Its a bit unclear (to me) what you are asking, can you provide a specific example with the specific aircraft involved. Based on the tag it seems like you want to know if you can get a rating for a DC-4 when no one at your operation is current on the aircraft. Do you cary a conventional gear checkout and multi-engine (thats the first step)

If I understand the question correctly;
Maybe
The FAA outlines a generic type rating curriculum in this AC which is worth going through as it outlines what training would potentially be required for the type cert,
FAA FAR 61.31 does allow for a waiver

§ 61.31 Type rating requirements, additional training, and authorization requirements.
(b)Authorization in lieu of a type rating. A person may be authorized
  to operate without a type rating for up to 60 days an aircraft
  requiring a type rating, provided -
(1) The Administrator has authorized the flight or series of flights;

(2) The Administrator has determined that an equivalent level of
 safety can be achieved through the operating limitations on the
 authorization;

(3) The person shows that compliance with paragraph (a) of this
 section is impracticable for the flight or series of flights; and

(4) The flight -

      (i) Involves only a ferry flight, training flight, test flight, or
      practical test for a pilot certificate or rating;

      (ii) Is within the United States;

      (iii) Does not involve operations for compensation or hire unless the
       compensation or hire involves payment for the use of the aircraft for
       training or taking a practical test; and

      (iv) Involves only the carriage of flight crewmembers considered
         essential for the flight.

(5) If the flight or series of flights cannot be accomplished within
   the time limit of the authorization, the Administrator may authorize
   an additional period of up to 60 days to accomplish the flight or
   series of flights.

Section 3 is the important one. You would have to show that it is "impractical" for you to obtain the type rating with out the waiver to operate the aircraft and fly the required training time.
You may also have a compounded issue of then needing a second crew member who is typed in the aircraft and can provide training/co-pilot duties. Further more you cant conduct any commercial operations while doing this so you need an empty DC-4 and a lot of time (read money) to fly it. Keep in mind you may only have 60 days to accomplish all the training as well or you will need to get an extension on the waiver.

Just a general note. These kinds of situations are often best suited for an aviation lawyer who has experience dealing with the FSDO. It would be wise in this case to seek the aid of someone like that. You also may want to look for remote training if there is another operational DC-4 flying elsewhere and an arrangement could be made for you to go train with them for some time that situation may, in the long run be simpler.

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What plane is this?
This aircraft was parked at the very back of the McCarran airport, and I was absolutely fascinated by it. It has a propeller on the back of the fuselage as well, though not very well shown in the picture.
What is its name or model?

The back propeller is visible in the first picture, under the letter N and number 6  , just barely visible. My apologies for the quality

Welcome to aviation.SE! For future reference, if you can see the registration (N number) clearly, you can always look it up in the FAA's database

BTW those are pretty good pictures considering you  had to stay outside the fence.

Having changed only the size of the images and making no difference to many people who can see them, the image descriptions have been removed, making them useless to those who can't. @kevin

The Military bought a bunch of these and used them as light observation aircraft in Vietnam and afterwards in the 70s and early 80s. The Military version was the O-2A. Two squadrons were formed in the CONUS, one at Bergstrom AFB in Austin, TX, and one at Shaw AFB (I think), in South Carolina.

Pro tip for future photographs: Hold the camera (phone?) right up to the fence and move until the lens is shooting between the links (do try not to scratch the glass against the fence). You'll get a much better image as it won't be trying to focus on the fence and the fence won't be a distraction in the image itself. Most point 'n shoots/cell phones have a wide enough angle lens that you'd have gotten the whole thing in from a few feet closer.

Googling the plane's registration number (this one is N6361F) is almost always enough to identify the plane.
In this case, FlightAware is high on the list of hits and says that the plane is a Cessna 337A, built in 1966.  Searching for "Cessna 337A" then leads to Wikipedia for more information.

That's a Cessna 337 Skymaster. They were built from the early 1960s to the early 1980s. Because the two engines are both on the fuselage centerline, the Skymaster is more controllable than a conventional twin engine aircraft in the event that an engine fails.

Plus great visibility for a twin.

IIRC, the military version of this had a distinguished history in Vietnam.

How would gyroscopic effects affect this sort of push-pull configuration vs conventional twin engine in the event of engine failure?

@Krumia That would be good as a formal question.

Cessna 337 Skymaster and/or the O-2.  The 337 uses a push/pull design which is rarely encountered, but gives you the advantage of centerline thrust in the event of an engine failure (but the disadvantage of a noisier cockpit).  You can see the military variant in the 1988 film Bat 21 with Gene Hackman and Danny Glover, some great aerial footage regarding the power and maneuverability of the aircraft.  Because of the push/pull prop design, some nicknamed it the "Mixmaster", but if you watch the movie Bat 21, you will see what a great aircraft it is despite the blender reference.

Also, for quick historical reference, although Cessna is known primarily as a civilian aircraft manufacturer, they have a history of producing aircraft that have seen combat such as the 337/O-2 above.  I flew the T-37 Tweet and T-41 Mescalaro, both Cessna products, in the USAF, and my former unit flew the A-37 Dragonfly variant of Cessna's T-37, many years ago, which is used as a low-cost ground attack aircraft to this day in several South American nations. Cessna also had an entry into the Tactical Surveillance role around 2013, just like the 337/O2 above, called the Scorpion.

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What is the ALT INTV on the 737's autopilot?
So, I was watching a quick tutorial on the FMC on YouTube. The FMC somehow had a 5000 ft restriction, and the guy got clearance to go higher up, and he set his altitude on the AP panel, and he pressed the ALT INTV button.

From the FCOMv2 4.10.10 (emphasis mine):

Altitude Intervention (ALT INTV) Switch
[Option - With speed and altitude intervention]
Allows manual deletion of next FMC altitude constraint via altitude SEL and ALT
  INTV switch.
Push – (during VNAV climb)

lowest FMC altitude constraint below selected MCP altitude is deleted
if airplane is currently at an FMC altitude constraint, deletion allows airplane to resume climb. MCP altitude must be set above current altitude
for each press of switch, one deletion occurs
if MCP altitude is set above current FMC altitude, FMC cruise altitude
  resets to MCP altitude. FMC cruise altitude cannot be decreased using
  ALT INTV switch.

Push – (during VNAV cruise)

if MCP altitude is set above current FMC cruise altitude, FMC resets
  cruise altitude to MCP altitude and initiates a cruise climb
if MCP altitude is set below current FMC cruise altitude, an early descent
  is initiated. Lower FMC cruise altitude cannot be entered using ALT
  INTV switch.

Push – (during VNAV descent)

the highest FMC altitude constraint above MCP altitude is deleted
if airplane is currently at an FMC altitude constraint, deletion allows
  airplane to continue descent. MCP altitude must be set below current
  altitude

[Option - FMC U10.6 and above]

if all FMC altitude constraints are deleted during VNAV path descent, an
  automatic transition to a VNAV speed descent is made.

It's quite simple to explain in laymen terms actually.
Before takeoff roll, the pilot input 5000 feet into the altitude window, then engaged VNAV1.
After takeoff, the plane will climb on the VNAV profile with an altitude restriction of "no more than 5000 feet", i.e. it will stop the climb and level at 5000 feet.
To climb higher, the pilot has to do two things:

Rotate the altitude knob to set the altitude window to a higher value
Push the "ALT INTV" button

If the pilot does not push the "ALT INTV" button, then rotating the knob has no effect at all. It is simply a command to tell the Auto Pilot to "execute" the new altitude restriction.

Here is more info about how the "ALT INTV" button is used.
You're cleared to climb to 5000 feet after takeoff (this instruction is given to you while you are still on the ground). You set the altitude window to 5000 feet, then takeoff. After a while, you are level at 5000 feet.
ATC clears you to 12000 feet. You rotate the knob to set 12000 feet, then push the button. The plane will now climb and level at 12000 feet.
Repeat until you reach cruise altitude.
On the way down, ATC clears to descend to FL 290. You rotate the knob to 29000 feet, then push the button. The plane will now descend from cruise altitude to FL 290.
Repeat until you are low enough to begin approach.
1: Technically VNAV can only be armed, but not engaged, while the plane is on the ground. It will automatically become engaged when the plane is 400 feet on the radio altimeter/AGL.

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What are the tube shaped structures on the back of the fuselage of this 737?
A previous question asked what the little metal plates between the horizontal and vertical stabilizer were (they are vortex generators), however I am much more interested in what the gray tube shaped structures are that go down the top quarter of the fuselage. What are they and what do they do? Are they sensors, countermeasure pods, something else?

The aircraft is the Indonesian Airforce Boeing 737-2X9 “Surveiller” aircraft, used for Maritime Patrol. The fairings house Side looking Airborne Radar for matitime surveillance. From b737.org:

Fitted with Motorola AN/APS-135(V) Side Looking Airborne Modular Multi-Mission Radar (SLAMMR) The antenna of which was mounted in two 16ft housings on the upper rear fuselage. This system could spot small ships at ranges of 100nm.

Indonesia Operates three of them- AI-7301, AI-7302 and AI-7303.

I like that acronym: SLAMMR. :D

@TomMcW It's a requirement to get military funding. :)


text:
Are military jets always scrambled when communication to a commercial aircraft is lost?
I've heard that in case a commercial flight does not respond to Air Traffic Control, military jets would always be scrambled to check the state of the flight.
The benefits of scrambling jets are clear. My question is, are they always scrambled in every case?

For reference, it seems that France has fighters on 7-minute alert unless something special is happening, so most of those 10 minutes would be just getting airborne.

Related: What's the point in escorting a threatened flight with two fighter jets?

Also related: What's the point of intercepting an aircraft? and How do fighter jets communicate with an intercepted plane that's lost comms?.

Hello algiogia, welcome to Aviation.SE. My initial reply was a bit harsh. There's been a lot of low quality content added here in the wake of the Germanwings crash. As a result a number of resident users here are getting a bit short-fused, including me. I am sorry you ended up on the wrong end of that, it is not the way I normally welcome new contributors here. The changes you've made to your question have greatly improved the quality. I vote to reopen.

@JanHudec the benefits of scrambling jets are clear. I was interested in knowing if it's always the case.

@DeltaLima yes, I've noticed :-) My question was actually meant to be more general, so I've edited

@ratchetfreak do you have any resource for that?

Hi algiogia.  @DeltaLima put it very well.  Just to add, as you rightly ask people to be nice to new users, you could be nice to everyone else by taking a little time to read the [faq] and [help/on-topic].  Welcome again.

Over Europe and many other parts of the world, the general rule is that if an aircraft in controlled airspace does not reply to instructions from Air Traffic Control, military jets will be scrambled to intercept the aircraft.
Basically you are asking if there are exceptions to that rule.
I think there are a few. First of all, ATC will not inform the military of every instruction that is not reacted to; there wouldn't be enough jets. Pilots do miss instructions occasionally, sometimes aircraft are handed of to the wrong frequency by ATC, wrong frequencies are entered into the radio etc. All these things usually sort themselves out in matter of minutes and it would be a waste of resources to scramble. If no contact is established after a certain amount of time, only then the military will be involved. However if an aircraft starts to deviate from earlier acknowledged instructions without reacting on the radio, it is safe to assume that the time to alert the military is considerably shorter.
And then of course the aircraft must be in range of military jets. An aircraft halfway across the Atlantic is simply too far out for most interceptors so until the aircraft is getting closer to shore I don't think there is much reason to scramble jets.
Some more information about loss of communications, causes and prevention  can be found in this Skybrary briefing note. For obvious reasons the exact procedures for scrambling military aircraft are not publicly available.

Aircraft over the Atlantic could be intercepted by jets launched from carriers, right? Of course, that depends on carrier placement (not exactly public information)

The Atlantic is not exactly a small pond and the range of supersonic interceptors is not very far. You need quite a few carriers to cover the it. There's not many places where you can force an aircraft to land either.

@raptortech97: Note that, to the best of my knowledge, there is exactly one country with more than a single carrier, and carriers spend a lot of their time in port or exercises where they are not particularly available for this kind of work, and most of the rest of their time in whatever "interesting" place benefits from their military presence, which is probably not bang in the middle of the ocean.

@NathanTuggy Wikipedia suggests that India, France, Italy, and Japan also have 2+

@raptortech97: I stand corrected!

@NathanTuggy: That list however includes helicopter ships that shouldn't be counted for this purpose. A carrier needs "CATOBAR" or "STOBAR" to be able to launch and recover supersonic fighters and of those types USA have 10 and any other country has at most 1. The "STOVL"-type ones can in addition to helicopter launch Hawker-Siddeley Harriers, but those are only a bit faster then transport aircraft and thus not really suitable for intercepting.

@DeltaLima do you have any source?

@algiogia Added a link. Googling for NATO QRA (quick reaction alert) might give some useful results if you want to investigate deeper.

@JanHudec: Then I guess I was right the first time. Ah well.

I remember reading an article a while ago about scrambling of aircraft in the UK; it made it sound like they received the order to scramble far more often than they took off (i.e., they'd be ordered to stand down before they'd got in the aircraft/started up/taxied to the runway). This suggests that at least in the UK aircraft are ordered to scramble relatively quickly.

There are well-defined procedures for communication loss and even for interceptions (at least in the US, but I guess other countries are similar). However those procedures are vague on when an interception is required:

In conjunction with the FAA, Air Defense Sectors monitor air traffic
  and could order an intercept in the interest of national security or
  defense. Intercepts during peacetime operations are vastly different
  than those conducted under increased states of readiness. The
  interceptors may be fighters or rotary wing aircraft. The reasons for
  aircraft intercept include, but are not limited to:
(a) Identify an aircraft;
(b) Track an aircraft;
(c) Inspect an aircraft;
(d) Divert an aircraft;
(e) Establish communications with an aircraft.

As you can see, there are no significant details there and certainly no one is saying that intercepts will always be ordered. But there are a couple of reasons why it's difficult to say anything more.
First, it's security-related, and the people who know the real answers won't give them anyway. See here for some related discussion.
Second, as this question explains, there are various reasons for launching jets: a political gesture, a demonstration of a country's military capabilities, and/or a piece of security theater. It's probably a safe bet that most developed countries have processes in place for when to launch an interception, but they certainly aren't public.

I would answer: No.  In the U.S. there is a "lost comm" procedure which is detailed in the Airman's Information Manual 6-4-1.  I this procedure, the crew should enter the lost comm code, 7600, into the transponder.  If in radar range, this signals to ATC that the aircrew knows that it's radio has failed, and ATC may presume that the crew will follow normal lost communications procedures.  As long as this is happening, and it looks like procedures are being followed, there is a good chance fighters will stay on the ground.  If, on the other hand, The crew keys in 7500, the hijack code, I would presume chances of a scramble are significantly elevated.
Basically the procedures look like this:

In Visual conditions, or if Visual conditions are encountered, land as soon as you can.
In instrument conditions, do your best to follow your flight plan as it was most recently cleared.

More details are in the manual.
It is interesting that there are a few ways to re-establish communications.  For example, ATC or flight service can utilize the voice feature of available navigation beacons, and may issue an instruction like, "Airline 1234, if you read, turn to heading 150."  If the crew can pick this up, they may be able to respond with a turn and they can continue from there.  The situation being under control, no need to send up interceptors.

Are military jets always scrambled...
Back to the question, NO.
Some regions are protected by armed platforms in continuous orbit.

I hear of planes being intercepted from time to time in many different regions, but have yet to hear of one being nuked from orbit.

I have yet to hear of an armed satellite of any kind, but then, I could simple be uninformed or perhaps I don't have a need to know.

I think he might have been referring to armed aircraft orbiting (as in circling or ellipsing) a high-value target, rather than literal orbiting satellites.  Especially since he emphasised "scrambled", strongly indicating that military jets are still involved - they just don't have to be scrambled (since they're already in the air).


text:
How does the head-up display on a spitfire work?
It turns out that the Spitfire from World War 2 had a head up display.
Does anybody know how it worked exactly?
All I could find was this picture, but no explanation:

Source
The source does not explain what it does.
Seeing as it is projected, it would only be of use if it were dynamic, that's why I'm asking.
How could they have something like that back in the day?
Edit: Not a duplicate, not all sights were gyro sights.

Possible duplicate of How did the gyro gunsights of WW2 get the range and lead of a target?

@Trevor I don't think it's a duplicate. This question asks how the optical system works; that question asks how the system figured out where the target is.

@DavidRicherby if he watches the video in my answer there it tells him,.

@Trevor What video? And I have to concur with DavidRicherby, that this is not a duplicate.

https://www.youtube.com/watch?v=DREz7qI8xRk the gunsite does not track the target, it projects where the guns are aimed in the sky, the pilot flys the aircraft and points it such that the target in that spot.

It's not a head-up display, it's a reflector gunsight. (Follow that link to learn how they work.) It just displays a fixed reticle to aim the cannon, not any flight instrumentation.
Some (but not all) Spitfires had a gyroscopic system to compute target leading and move the position of the reticle appropriately, based on the speed of the aircraft; I suspect that your photo is of this equipment, and that's what the range adjustment visible at the bottom is. More about that can be found at How did the gyro gunsights of WW2 get the range and lead of a target?

Seeing as it is projected, it would only be of use, if it would be dynamic, that's why I'm asking.

That's not actually true. A "static" reflector gunsight is hugely advantageous over a collimator sight (i.e. a tube that you look through) or iron sights, because the crosshairs still appear in the correct place when you move your head. Early aircraft machine guns used collimator sights, but you have to hold your eye right up to the sight to see through it. This often resulted in injuries if the aircraft jerked at the wrong time. Iron sights were subsequently popular, but you still need to line up with the sights correctly, which is time you don't want to spend in a dogfight. With a reflector gunsight, the image of the crosshairs moves as you move your head, so you only have to glance in the correct direction to line up the shot. That's why they're also popular on small arms nowadays.

Wow, that's serious technology for that time!

@mike: Yes, it was. When gyro gunsights started appearing as standard equipment on British and US aircraft in early 1944, they increased the probability of hits significantly. The Luftwaffe designed a somewhat superior gyro sight, but were unable to produce it in quantity.

@mike: What continually amazes me even more is that on WWI planes (1915 and onwards), they already had devised a way to shoot the gun through the propeller without hitting the blades. Link. That's 25-ish years earlier than the Spitfire's reflector gunsight, and only a mere decade after the Wright brothers' famous first flight (= 1903)

I don't understand the point about the collimator sights. The point of a collimator is to allow the free movement of the eye and still show the crosshair at the right spot. In my language "kolimator" means a reflector sight for firearms.

authors: Vladimir F Героям слава


text:
How do blimps control altitude?
If you have an airship filled with helium, how can you adjust your altitude?  i.e. how do you "go up" or "go down"?
Even staying still would be a challenge: The way I see it, you'll never have exactly the same average density as air and therefore will always be either slightly falling or slightly rising.
Is it the case that they have an extra tank of compressed gas as well as vents on the blimp and they make adjustmenst by increasing/decreasing internal pressure of the balloon?

An airship pilot has three ways of adjusting lift:

Every lighter-than-air vehicle needs some ballast to adjust its weight. This could be sand, but mostly water is used.
A blimp is only partially filled with helium. The envelope is held taut by filling a bag inside with air, called a ballonet. If you press a little more air in this bag, the overall density of the gasses in the envelope goes up, while the volume stays practically constant. This allows for fine adjustment. Forward and aft ballonets even allow for trimming the pitch attitude.
When the airship moves, the air does provide a little dynamic lift or downforce, depending on pitch attitude and elevator deflection. This is a little tricky, because airships are not stable, and a pitch-up command will lead to altitude loss below a critical speed.

The ballonets in this cutaway drawing of a Goodyear blimp are numbered 2 and 4.
On a calm day, the biggest disturbance is actually the sun. If the envelope is exposed to direct sunlight, it will heat up and the gas within will be heated as well, causing the blimp to rise. If the sun is covered by a cloud, the gas cools down and loses some lift. On partially cloudy days it is not easy to keep the same altitude!
Another threat is an unstable atmospheric temperature gradient. Glider pilots love this, because it will give them strong thermals, but the gas inside the airship will behave similarly to that bubble of warmer gas which causes thermals. When the airship rises, the gas inside cools less quickly than the surrounding air, and the airship will gain lift when it goes up. It becomes really bad on the way down: Now the gas warms up less quickly as well, and the airship loses lift as it comes down. The airship pilot needs to drop some ballast or create more dynamic lift, or his craft will slam into the ground.
Long-range airships like the LZ-127 used a mixture of hydrocarbon gases as fuel. This mixture (called Blaugas) was balanced to be just as heavy as air and filled some of the gas cells within the envelope. Consumed fuel would be displaced by air, so no lift adjustment was needed on a long trip.

According to a CarTalk (US radio program) puzzle, during World War II the Germans invented a condenser which would capture from the exhaust of burning gasoline a mass of water roughly equal to the mass of fuel burned.  I wonder if that concept would still be practical?

@supercat: The last Zeppelins were wrecked in 1940 - so that was way before WW II. Yes, that technique was indeed used on gasoline-powered long-range Zeppelins, and it would be practical if blimps would travel at higher speeds and for longer durations. Today, fuel consumption is not high enough to make the additional mass of the condenser system worthwhile.

Epic answer, thanks man!

@DavidRicherby: Thank you for the editing! I knew something was looking odd with that word, but I couldn't tell what it was.

Inside the airship are ballonets that are filled with air. These can be easily inflated with compressor and deflated to outer atmosphere without wasting the precious lifting gas, especially in the new designs where the lifting gas is usually safe but expensive helium.
In non-rigid and semi-rigid ships the ballonets are inside the gas cell. In rigid ships the ballonets were between the gas cells and were together with them constrained by the outer shell.
There are normally at least two ballonets, fore and aft, to provide pitch control.
As for altitude control, airships are actually stable in altitude. As the ship ascends, the shell does not allow the gas to expand as fast as the outer pressure declines, therefore reducing buoyancy. Of course as fuel is burnt, weight decreases and the pressure needs to be adjusted accordingly to maintain altitude.
Many airships also have swivelling engines allowing additional up or down thrust.


text:
What would happen if I bank a helicopter then pull hard on the cyclic?
Prompted by Simon's response to my question here, I will ask another question about reality.
If I:

Start with a AH-6 helicopter in a hover
Pitch down slightly to accelerate, then slowly increase collective to gain speed until max collective is applied and the airspeed is near Vne
Roll the helicopter to about 70 degrees of bank
Pull back hard on the cyclic

(Basically it can be described as trying to fly a Red Bull race in a helicopter)
What would happen?

I doubt these are attempted anywhere Vne, but it is pretty cool to watch the Redbull Helicopter do things no other helicopter can do, including extreme bank (complete rolls).

Possible duplicate of Can a helicopter stall?

Not a duplicate at all. This question asks about maneuvering a helicopter near Vne at an extreme bank angle.

Are you trying to stay in a level turn at 70 degrees AOB?  Are you familiar with the term "retreating blade stall" as it applies to helicopters.

What does max collective mean?  Max permiites lower, lever fully up or something else?

@Simon collective up, max lift demanded from the blades.

Collextive all rhe way up does not equal max lift. Do you mean pulled all the way up or max aerodynamic lift?

@Simon hmmm, I used to think pulling it all the way up would imply max lift. The objective is to fly as fast as possible, which I think (correct me if I'm wrong!) is accomplished by demanding max lift from the blades, then pitch down just enough to convert lift into forward thrust without gaining or losing altitude.

I can't provide references specific to this manoeuvre. The main texts on helicopter dynamics only generalise since such a manoeuvre isn't flown in real life or tested during certifications.
When you raise the collective, you increase the pitch of the all of the blades together.  In most flight regimes, this means increased angle of attack and therefore lift.
The cost of producing lift is drag which always increases.  So, there is a direct relationship between the collective lever and power required from the engine.
As you continue to raise the collective, AoA and lift will increase until you reach a point where the power required to overcome drag exceeds the rated power of the engine.  Most helicopters permit operation beyond the maximum for a short time, e.g. 2 or 5 minutes, typically during take-off.  Continue to increase AoA beyond this limit and drag will exceed power available and the rotor RPM will drop (a reduction in rotor RPM caused by drag exceeding power through too much collective is known as "droop").
As RRPM decreases, so does lift and the helicopter will descend.  The relative airflow into the disk now has a greater horizontal component and the angle of attack will increase, either causing yet more drag or stalling the rotor.
So there is some point, before the collective is pulled fully up where maximum lift is attained.  Beyond that, lift reduces until recovery or a stall.  The only time I have ever raised the collective fully is during "full and free" movement checks with the engine off as part of pre-flight.
Your hypothetical manoeuvre:
From VNE in level flight, you roll into a 70 degree bank.
The TRT( total rotor thrust) is always acting perpendicular to the plane of the rotor disk.  Since you are in a bank, and I assume it is at constant altitude, there is a large horizontal component of the TRT to maintain the acceleration in the turn and a large vertical component to oppose gravity and maintain altitude.
This requires a lot of power which means a lot of collective and a lot of drag.  I don't know for the AH-6, maybe there's a chart relating bank angle and speed to power but let's just say, your collective is going to be somewhere near the max lift point with a manoeuvre like this.
Since you are now accelerating with max power, your speed will decrease.  Therefore lift will decrease and since you are at or near max power, you will begin to descend.
So far, this is probably recoverable simply by rolling level and reducing collective until back inside the performance envelope.
The second part is where it definitely will go wrong. In all helicopters with a non-rigid head, including the AH-6, the disk will adopt a new plane of rotation rapidly.  There is then a significant delay before the fuselage adopts a new attitude which puts the TRT perpendicular with the aircraft Z axis.
Pulling hard on the cyclic will very rapidly put the disk into a new plane of rotation which has a large angle between the plane of rotation and the fuselage.  Additionally, the disk loading will increase dramatically and the blades will be forced downwards.  On an articulated head such as that on the AH-6, droop stops will prevent the blades from bending down so much that they fold.
Hitting the droop stops a little is uncomfortable with a lot of vibration. Pulling hard on the cyclic at VNE in a 70 degree bank at or near max power may cause failure of the droop stops or blades or cause the static droop stops to contact the  mast possibly leading to rotor separation.
Let's assume that there is no failure.  The plane of rotation will be at the maximum permitted by the physical limits of the flapping hinges which is greater than the angle between the plane of rotation and the fuselage.
Therefore, I would expect a hard pull on the cyclic to result in a blade hitting the tail or the top of the cockpit.  Either results in destruction of the aircraft, either as it breaks up at that point or when it hits the ground 10 seconds later.

First post here. I'm not a pilot, but this is how I see it happening with my understanding of helicopter forces.
Collective is up a fair bit since we've been raising it.  VNE is approaching fast, and we may be starting to feel a retreating blade effect, so we might be naturally pitching left ever so slightly.  If we propogate that to 70 degrees, then quickly pull back hard on the cyclic, with the collective never changing, the main rotor will pitch up in front and down in back to an extreme, and the blades will slow down considerably with all that drag.  You will also experience inverse torque and your hull will begin to twist right abruptly unless extreme action is also taken on the rudder, throttle, and collective to mitigate the sudden change in vector momentum.  You will also pitch wildly to the left even more, which will further confuse your vector of travel, adding strain on your hull, main rotor, and drive shaft.
Imagine pulling up, tilting left, and spinning right.  Now you're sort of flying sideways/backwards, ~270 degrees from your previous travel vector, and still spinning your hull to the right.


text:
What are the Autopilot Minimums for a C-172 G1000?
(GA Pilot)
On a C-172 (G1000 Avionics), what would be the AutoPilot minimums OR at what altitude would one need to disengage the auto-pilot and take controls for:
1) Precision Approaches
2) Non-Precision Approaches
3) Visual Approaches ..?

Where in the world are you? Approach minima vary around the world...

As UnrecognizedFallingObject brought up, please edit your question and specify whether you are looking for an answer for an aircraft certified and flown under FAA, EASA, etc. rules as this will change the answer.

Typically, the aircraft flight manual will identify this. In your particular case (Cessna 172 G1000), it is 200 feet AGL for all approach types.
The C-172 can be fitted with either a Garmin GFC 700, or a Bendix/King KAP 140.
For the GFC 700, it is listed in the aircraft operating limitations:

In the case of the KAP 140, it is listed in the autopilot supplement:

This may vary depending on where the aircraft was certified (the POH is written for the appropriate certifying authority) AND it also varies depending on the regulations....

That answers my question - thank you!


text:
What direction should a traffic pattern be at an uncontrolled or non-towered airport?
What is the standard direction for a traffic pattern at an uncontrolled or non-towered airport?

possible duplicate of Traffic pattern required with no traffic at untowered airport?

I disagree that it's a duplicate. This question simply asks which direction that traffic patterns should be flown. The other question asks if it's okay to fly a straight-in approach. They have a similar answer derived from the same regulation, but it's not a duplicate.

When aviation literature mentions "the standard traffic pattern", it's usually a left-hand counterclockwise pattern; regardless of wind direction, the runway will always be to your left side and you make left turns to follow the pattern through crosswind, downwind and base legs. This is the default pattern direction when there are no overriding signals.
However, this is only the default, and airports are free to change the procedure as needed to comply with local terrain or development. An airfield near a neighborhood to its east, for instance, may require that traffic circle around the west side of the airport; therefore this airfield's 17/35 runway will require a left-hand pattern when using runway 35, but a right-hand pattern when using runway 17.
When an airfield establishes a non-default traffic pattern, they must provide this information to pilots in a readily-visible manner. The standard recommended (though not required) set of runway and pattern indicators is known as the segmented circle, so called because its most visible identifying feature from a distance is a 75-foot circle of dashed lines:

In the center of the circle as pictured is the runway direction indicator aka the tetrahedron; this will indicate which strip of asphalt to use and which direction to take off and land on it (the narrow end points in the direction that planes should take off and land).
Off to one side is the windsock, which is the only piece of equipment that is required at any airfield; it indicates approximate wind speed and direction. FAA guidelines for the sock say it should reliably turn to the wind direction at 3 knots, begin to inflate at 5 knots and be fully extended at 15. The windsock can replace the tetrahedron in the center of the circle; in that configuration you would simply approach the airfield using the runway closest to the direction in which the tip of the windsock is pointing (if winds are calm and/or the airfield has multiple runways, the tetrahedron is preferable).
On the ground just outside the segmented circle are L shapes; these are the pattern indicators, and point in the direction of the base leg when approaching the runway from that end (so if you're following the pattern, the end of the L should be pointing at you before your turn to final).

So, the circle in the above picture tells aviators several critical things without any human (or computer) having to relay the information vocally:

The approach direction is from the upper right to the lower left of this picture.
The wind is roughly in line with the runway, so no crosswind landing procedure is required.
Winds are very strong (the windsock is fully extended which indicates wind speeds in excess of 15 knots) so ground speed will be much lower than IAS at takeoff and landing.
Most relevant to your question, airfield traffic should be on a right-hand pattern at this time; if the winds and thus the runway in use were opposite, traffic would use a left-hand approach.

IDK about a wind sock being required.  I've landed at a number of strips in the western US that didn't seem to have one.

FAA Advisory Circular 90-66b
Title: Non-Towered Airport Flight Operations
3/13/2018

9.1 Left Traffic. Use of standard traffic patterns (left turns) for all aircraft and CTAF procedures by radio-equipped aircraft are
  required at all airports without operating control towers unless
  indicated otherwise by visual markings, light gun signals, airport
  publications, or published approach procedure. It is recognized that
  other traffic patterns (right turns) may already be in common use at
  some airports or that special circumstances or conditions exist that
  may prevent use of the standard traffic pattern. Right-hand patterns
  are noted at airports on an aeronautical chart with an “RP” designator
  and the applicable runway next to the airport symbol.

FAR 91.126(b)(1) states that all turns in the vicinity of an airport in Class G airspace should be made to the left unless otherwise marked. That includes the traffic pattern.

That's not quite what it says: turns to the left "when approaching to land".


text:
What is a radar fix?
Sometimes fixes found on approach plates are labeled radar. What are these radar fixes and how to they differ from fixes usually found on approaches?

I know from experience that minimally equipped aircraft can have ATC identify these fixes from radar, but I'm not sure where the concept of a radar fix on an approach is documented by the FAA. I also assume that in the real world most aircraft are able to identify these fixes on their own, but when is it legal to do so?

Since this an FAA instrument approach procedure, this answer is specific to the FAA.
The RADAR label indicates that these fixes are marked on the approach controller's screen and he/she can advise the pilot when the aircraft is over the fix.
The use of Radar for arrivals and approaches is outlined in FAA JO 7110.65, Chapter 5, Sections 9 and 10. FAA Order 8260.19, paragraph 8-2-5(a) states that "Radar vectoring may be provided through any approach segment up to and including the final approach fix."
You'll note that the approach plate does NOT indicate RADAR REQUIRED because it is not the only method of determining or defining the fixes. In this particular approach, arrival at a fix can be determined THREE different ways: with Radar, LOC with DME (or GPS lieu of DME), and LOC with VOR radial. Per 8260.19, paragraph 8-6-6h, all IFR aircraft are assumed to have at least one VOR receiver, thus no equipment requirement note is required for this particular approach.
In practice, I've found that ATC will not call out crossing a fix unless you specifically request the service, though they will usually identify your position prior to hand-off (e.g. November 1234, two miles from SHAGY, contact tower on 120.5).

If you asked ATC to identify the radar fixes for you, would the approach controller or the tower controller do that for you? I want to say the approach controller, but you're in a high workload environment, and you would have to tell tower if you had to go around. Also, AFAIK, most towers don't have their own radar.


text:
Anyone recognize this airport?
I found this image on boldmethod.
Where is this? Looks like a beautiful place. Has an instrument approach (from the runway markings.) On a mesa in snow country. It is not Sedona or St George.
Telluride?

Where did you get the picture from?

I found the image on BoldMethod. The credit is themselves, but I imagine an email to the article author might yield a result.

Please include source information in the post. @CatchAsCatchCan are you the same person as "dawg" the OP?

*@CatchAsCatchCan are you the same person as "dawg" * -- No, I am not @CatchAsCatchCan. I am sure he did a google image search. Yes, that is the source of that image.

@FreeMan No, I'm not dawg, and yes, I did a Google image search

Well done, then, @CatchAsCatchCan!

Yes, Telluride RWY 9, as can be seen clearly in this video.
Screenshot from video:


text:
KSEE LOC-D conundrum
Consider the LOC-D at KSEE and note the Alternate Minimums criteria.

99.9% of the time, the winds strongly favor 27R;
The tower closes at 1900 PT currently (usually at 2100 PT non COVID times);
LOC-D is a circle only approach with a 6.88º final segment;
LOC-D to 27R not available to at night at all I think since it is a circle only approach (given the steepness). However, you can cancel IFR and continue visually usually;
DEBEY to Apt Elev in 3.1 nm is over 1,500 ft / min descent rate at 120 kts (top of Class B approach speed and common for a small turbo jet aircraft such as a Phenom)
Stabilized approach criteria for a Phenom is no more than 1,000 ft / min decent rate within 1,000 ft of the ground;
Circle NA with tower closed or to the northeast;
Local custom is to start on the LOC-D approach and cancel IFR prior to DEBEY. That makes the approach a 2,400 and 3 mi approach.

With the following conditions:

Part 91 in a light turbojet, class B aircraft (a Phenom);
Night with 1,800 Broken / 3 (so below the altitude at DEBEY and beyond where it is practical to cancel IFR even though KSEE is VFR);
Wind from the west at 10 kts (most turbo jet aircraft have a 10 kt tailwind limitation including the Phenom);
Tower closed (so no circle to land 27R) and Class G around KSEE;
There are two RNAV approaches to 9L and 17. If you do one of these, you still have the 27R circle limitation for night and tower closed but they each have lower minima. 17 / 35 is 1200 feet shorter with a cross wind. 9L would have a limitation busting tail wind.

Questions (and my concern are the REGULATORY aspects here) with the airport 1800 and 3:

Can the LOC-D be flown with the tower closed at all? (The Alternate Minimums clearly state Circling is NA with the tower closed and LOC-D is a circling only approach. But aircraft are commonly cleared LOC-D approach with tower closed...)

Can you land on 27R with some interpretation of IFR rules?
a. If you fly LOC-D with with tower closed, is completion of that approach NA? As a practical matter, on LOC-D, you would break out at 1800 about 1.5 miles from the airport decending at 1500 fpm at night trying to break in to cancel IFR with SOCAL... You can descend to a VFR pattern height and complete the pattern VFR and buy time to cancel.
b. Can you fly one of the approaches and cancel IFR and complete the approach VFR?

What are the limitations on when during an approach you can cancel IFR and legally complete the approach VFR?

Alternative #1: does your landing performance allow landing on 19, even though it is short?  Alternative #2: tell the customer he can choose between going to El Cajon during daylight or to Lindberg at night -- his choice.

There is only 27R / 9L or 17/35. Did you mean 17? As stated, 4100 feet is shortist at night with 10 kts cross wind, but doable. Better alternate is KMYF than KSAN.

Sorry, 17.  Since the performance supports that runway, it's an option; maybe see about getting some practice landing on something similar (comparable width + lighting, longer but with a visible spot to see what 4100' down is) at night to build proficiency. And until the pilot is comfortable with that operation, offer the customer his other options.

Maybe I did not make clear that my interest (and concern) is the regulations and limitations (10kt tailwind) and SOPs vs proficiency. I already feel quite proficient to land on less than 4000 ft at night and regularly land at SMO (3500 ft).

Example concerns: Is my interpretations that ANY circle from ANY approach landing 27R or 35 is prohibited with the tower closed yet (as a local at KSEE) they are regularly flown with the tower closed? Is the regulatory interpretation that those landings are VFR procedures since they cancel IFR on the LOC-D? A practical alternative: If minimums are below 2700 but  above the 1720 of the new RNAV 9L can you make that approach, start and circle, cancel IFR and continue VFR for the landing 27R? Is there limitation WHEN you can cancel IFR to fall back to VFR landing criteria? The airport is 1800/3

I am imagining that there is AC on this. I just can't find it!

Sounds like you're looking (hoping?) for the possibility that cancelling IFR at the right moment after you've flown the approach & are in VMC makes it ok to fly, under VFR, what would otherwise be prohibited as "circling at night" but now legal as a VFR traffic pattern. I'll leave the legality answer to somebody else, but remember: the prohibition on night circling exists for GOOD REASON. While familiarity with the airport does give you better awareness than somebody arriving there for the 1st time, that doesn't remove the terrain + associated risks that drive the "NA". Even if legal... safe??

Well yes, but actual circling minimums are lower (1.5 mi visibility and clear of clouds) than the applicable night Class G requirements (3 mi visibility + 500/1000/2000 cloud clearance.) I am not trying to game it; I am trying to comply with it.

Alt Mins are only when you’re filing it as an Alt. You can still file it as your Dest.


text:
Why are "counterweights" used in aircraft production?
From this question, manufacturers use "counterweight" or "ballast" when producing aircraft. Why is the use of weight necessary? Supposedly aircraft should be made as light as possible, and counterweight is just dead weight without any function.
I presume it is used to balance some centre of gravity, but why would that be necessary? With industrialized factories, components can be engineered to great accuracy, so a case-by-case adjustment to account for manufacturing errors should not be needed.

The counterweights in the original question were from a Boeing 747 rudder, so I will explain what their purpose is. John Walter's answer covers all applications of balances and ballast well enough, so I just want to explain why control surfaces need balances.
The short answer is: To bring the center of gravity on or even ahead of the elastic line of the control surface in order to limit gust loads and suppress flutter. The same is achieved for the full wing when jet engines are placed ahead of the wing.
First consider an aileron without a balancing mass. Its elastic axis is the hinge line and its center of gravity is maybe at a third of its chord, so it sits aft of the elastic axis. Now imagine what happens when the aircraft to which this aileron is attached flies through a positive gust: The wing bends up and inertial loads will keep the aileron from moving up with the wing. However, since it is attached to the wing at the hinge, its forward edge will be pulled up, resulting in a positive aileron deflection. This adds local camber and increases local lift, so the bending motion is intensified. At some point the wing stops moving up and the stored elastic energy reverses the bending motion: The wing starts to move down, and again will the aileron lag behind, now reducing local lift and again intensifying the bending motion. Watch this movie to see the resulting motion (the scary stuff starts at 2:40):

Now you might argue that in the 747 strong hydraulic cylinders keep the aileron from moving: Right, but still there is enough elasticity in the control system to let the aileron move a few degrees, which is enough to amplify the bending motion. The glider in the movie had high-aspect ratio wings of a rather elastic material (glassfiber-epoxy), so it flutters at a low speed where the energies and frequencies are low. Nevertheless, after the movie was filmed it had to be overhauled: The control fittings were almost completely worn out.
Now consider the same arrangement, but with balancing mass: The aileron will either stay neutral, if its center of gravity is in the elastic line, or will even counter the bending motion if the center of gravity is ahead of the hinge line. Both peak loads and flutter risk will be reduced. More agreeable control forces are just a side effect; the main reason is to keep the control surfaces or even the whole wing from breaking off.
The mechanism is the same for the rudder, but here the elasticity comes from the long fuselage tube which will be twisted by the side loads on the vertical tail. Again, only with enough balancing mass will the self-reinforcing nature of a twisting fuselage that swings the vertical tail left and right be avoided.

So in the video was this just a gilder with the balancing mass removed? How did they get the extreme flutter?

@curious_cat: Yes, there was balancing, but too little. The pilot flew at the right speed (90 km/h) and gave the stick a sideways jerk and then let go of the stick. The rest happened all by itself. The basic design hat flown before without flutter, but with 18m wingspan. The next wing was built in a similar way, but extended to 22m. That was all it took to get this extreme flutter.

@PeterKämpf - good comments on the flutter factor....

In the context of aircraft design and maintenance, the terms counterweight and ballast generally have separate and different meanings.
Both concepts involve mass used to balance, dampen, or adjust forces about a rotational axis. While ballast could also be described as a type of counterweight, it is best understood as working within the frame of reference of the entire aircraft since it adjusts the aircraft Center of Gravity (CG). Conversely, counterweights can be understood to work within a frame of reference that is smaller than the aircraft as a whole, such as an engine or a control surface.
I will address each separately.
Counterweights
Counterweights primarily serve three functions in aircraft design: balancing control surfaces, controlling propeller pitch, and balancing crankshafts in piston engines.
Control Surfaces
Counterweights are used to balance control surfaces about the axis of the hinge to avoid potentially dangerous control flutter. This balance is very important. Pilots typically check for counterweight structural security in preflight where able. Mechanics must recheck control surface balance after painting, and painting control surfaces is excluded from the list of preventative maintenance items that an aircraft operator can perform without a mechanics license.
From the A&P Mechanics Airframe Handbook AC65-15A:

It is this out-of-balance condition that can cause
  a damaging flutter or buffeting of an aircraft and
  therefore must be eliminated. This is best accomplished
  by adding weights either inside or on the
  leading edge of the tabs, ailerons, or in the proper
  location on the balance panels.

The following excerpt from the Cessna 172M IPC shows the elevator counterweights, 23, highlighted in blue:

Propellers
Counterweights are used in some constant speed propeller designs to increase the pitch of the propeller blades. Engine oil pressure is used to overcome the force of the counterweights to move the propeller blades back to fine pitch. In feathering designs, the counterweights assist in moving the blades to the feathered position.
From the A&P Mechanics Powerplant Handbook AC65-12A:

Propellers, having counterweights attached to the blade clamps,
  utilize centrifugal force derived from the counterweights to increase
  the itch of the blades. The centrifugal force, due to rotation of the
  propeller tends to move the counterweights into the plane of rotation,
  thereby increasing the pitch of the blades.

Feathering is accomplished by releasing the governor oil
  pressure, allowing the counterweights and feathering spring to feather
  the blades. This is done by pulling the governor pitch control back to
  the limit of its travel. which opens up a port in the governor
  allowing the oil from the propeller to drain back into the engine. The
  time necessary to feather depends upon the size of the oil passage
  from the propeller to the engine, and the force exerted by the spring
  and counterweights.

AC65-12A Fig 7-11:

Crankshafts
Counterweights are used in piston engines for both static and dynamic balancing.
From the A&P Mechanics Powerplant Handbook AC65-12A:

Crankshaft Balance
  Excessive vibration in an engine not only results
  in fatigue failure of the metal structures, but also
  causes the moving parts to wear rapidly. In some
  instances, excessive vibration is caused by a crankshaft
  which is not balanced. Crankshafts are balanced
  for static balance and dynamic balance.
  A crankshaft is statically balanced when the
  weight of the entire assembly of crankpins, crank
  cheeks, and counterweights is balanced around the
  axis of rotation. When testing the crankshaft for
  static balance, it is placed on two knife edges. If
  the shaft tends to turn toward any one position during
  the test, it is out of static balance.
  A crankshaft is dynamically balanced when all
  the forces created by crankshaft rotation and power
  impulses are balanced within themselves so that little
  or no vibration is produced when the engine is operating.
  To reduce vibration to a minimum during
  engine operation, dynamic dampers are incorporated
  on the crankshaft. A dynamic damper is merely a
  pendulum which is so fastened to the crankshaft that
  it is free to move in a small arc. It is incorporated
  in the counterweight assembly. Some crankshafts
  incorporate two or more of these assemblies, each
  being attached to a different crank cheek. The
  distance the pendulum moves and its vibrating frequency
  correspond to the frequency of the power
  irnpulses pf the engine. When the vibration frequency
  of the crankshaft occurs, the pendulum oscillates
  out of time with the crankshaft vibration, thus
  reducing vibration to a minimum.
Dynamic Dampers
  The construction of the dynamic damper used in
  one engine consists of a movable slotted-steel counterweight
  attached to the crank cheek. Two spoolshaped
  steel pins extend into the slot and pass
  through oversized holes in the counterweight and
  crank cheek. The difference in the diameter between
  the pins and the holes provides a pendulum
  effect.

From the Continental O-300 overhaul manual:

C-145 and 0-300 crankshafts have a blade extending from each side of the cheek between No's 1 and 2 crankpins for attachment of dynamic damper counterweights. Each blade has two holes bored through and steel bushed. Slotted counterweights fit over the blades and have holes bored through and bushed to match those of the shaft. Bushings are sized to produce the desired frequency.

The following shows those counterweights on an O-300 crankshaft that is apart for overhaul:

Source: own work

Ballast
Ballast provides a temporary or permanent change to overall aircraft center of gravity. Ballast might be included as a permanent part of an initial or modified design. When I was in flight training we used old aircraft tires filled with concrete as ballast to place the W&B of a U206G near a max gross weight and aft CG configuration for portions of mountain flying training.
I know glider pilots use ballast for adjusting aircraft CG as well.
From the A&P Mechanics General Handbook AC65-9A (this AC is cancelled, but this comes from my old print edition and is still accurate):

Ballast is used in an aircraft to attain the desired c.g. balance. It is usually located as far aft or as far forward as possible to bring the c.g. within the limits using a minimum amount of weight. Ballast that is installed to compensate for the removal or installation of equipment items and that is to remain in the aircraft for long periods is called permanent ballast. It is generally lead bars or plates bolted to the aircraft structure.

Temporary ballast, or removable ballast, is used to meet certain loading conditions that may vary from time to time. It generally takes the form of lead shot bags, sand bags, or other weight items that are not permanently installed.

I think the OP meant ballast not counterweights.

Aren't counterweights used in propellers to balance them with each other so they don't vibrate? Or do they use the same system helicopter and fan blades use where they can move a little bit to find the balance point?

My answer now addresses both, so regardless of what he meant it should be answered now.

@TomMcW Propellers are statically balanced before installation. Very small balance weights can be installed, but in my experience removing a small amount of material is more common.

Isn't ballast where they use / used to use depleted uranium?

@curious_cat Maybe, but not that I am aware of. The only aircraft use of DU that I am aware of is/was for control surface counterweights, such as in the B747 elevator.

In the past (aircraft manufactured before 1993): Depleted uranium used in the tails of Boeing 747s. Which can add to the tragedy of a crash: DU: A BURNING ISSUE. Bulk depleted uranium is not a problem - a thick layer of sticky tape is sufficent shielding from the alpha particles to pick up a bar of it and be very surprised at its density.

@AndrewMorton Nitpicky question. How do you first put the sticky tape on?

@curious_cat: Gloves. Alpha emitters are chiefly a problem when they enter your body, e.g. if you were to breathe the smoke released by burning DU. So the gloves aren't really needed to protect your hands from radiation, it's to prevent particles getting stuck to your hands and then being carried off.

@curious_cat Find the end of the sticky tape before putting the gloves on.

Given that depleted uranium has flammability issues, I would of thought that Tungsten would be the material of choice. It is slightly denser to boot.

@jCisco Though that is the case, I would presume that economic considerations likely played a more significant role in the decisions to use DU over Tungsten.

Beyond the description be @Jonathan Walters there is also the requirement to put the center of mass of the entire aircraft within margins.
In a typical airliner you are limited in how long you can make the tail before you run the risk of tail strikes but less on how long you can make the nose.
So a relatively simple measure to get more cargo room is to lengthen the hull of the aircraft in front of the wings.This puts more weight forward of the wings and rear landing gear decreasing its ability to fly and its ability to actually put cargo in the newly created space. Then if you counterbalance that with weights in the tail you can put more cargo into the front section and still do a proper takeoff.

Do you know if this lengthening of the fuselage in front of the wings thus necessitating use of ballast something that has been implemented in aircraft undergoing a lengthening redesign (i.e. MD-90), or is it something that has been implemented in an original design?

Counter Weights are used to provide offset forces in the flight controls.
This provides controls with better "feel" and "feedback" forces as well as reducing the required pressure to move the controls.  This is also done with "tabs" that use air pressure for the similar reasons. It is also helpful in mitigating flight control flutter or vibration that can occur at certain airspeeds, flight control positions and attitudes with some aircraft.
Ballast is used to balance the airplane for better control and stability during flight.  This is critical because its impossible to build an airplane that is perfectly balanced where you want the center of gravity to be.  Many other factors, besides the actual airframe, affect the center of gravity: seating, installed avionics and other installed features or equipment.  All of this must be taken in to account for the airplane to have an appropriate starting center of gravity.
I have flown numerous aircraft ( light aircraft as well as small to medium sized jets ) that required additional ballast to offset imbalances in cargo or where passengers where sitting or just to balance the aircraft better when it was empty or had equipment or seats removed or just didn't have any passengers at all.  I would sometimes use 25 pound bags of "Lead Shot" used for reloading shotgun shells as ballast in the aft cargo hold ( again this was in smaller aircraft such as private jets ).  this might be 100 - 200 pounds as far aft as it could be placed to provide as much leverage as possible, as needed.
As far as trying to keep an airplane as light as possible, this is true, however, it is so critical for the aircraft to be "balanced" and is so impossible to do this through structural changes that the cost in weight of the counter weights or ballast is not a factor.
Former Fighter Pilot and Private Jet / Corporate Jet Pilot

A few months ago I observed a Delta pilot call for 700 pounds of ballast.  The ground crew then hauled out 7 big bags of ballast in what looked like industrial-strength sandbags and placed them as far back in the rear luggage area as possible.  This was most likely a CRJ-200, but I didn't note for sure the specific aircraft.  It did not seem to be an unusual request to the ground crew.
A question - do smaller jet aircraft such as the CRJ-200 have some sort of automatic balance readout for the pilot, or does the pilot need to do manual calculations to know how much ballast is needed?

@ScottEvans Your question might be best asked as a new question on this site if it hasn't been asked already. It sounds like it could be a good question! Also, Delta pilots do not operate any of the CRJ series. This was probably a regional airline operating as Delta Express, or similar.

@ScottEvans sometimes the pilot just uses Mk.I eyeballs. I've been in an 8 seater corporate jet where before takeoff we got the instruction "It's a bit windy and bumpy today, folks, so can we have the heaviest guys sitting in the front seats please." ;)

@ScottEvans the pilots always calculate the weight and balance and would have done so in this case - its routine.  The CRJ was likely very light on passengers as empty aircraft of that type are designed to be in the best center of gravity condition with passengers and when empty often have a CG that is way too far forward.  They may also be so experienced with that airplane that they already know from so many previous calculations what they need in ballast under certain conditions.

@ScottEvans - also, There are no automatic readouts for CG in the A/C.  That type of thing would be far to unreliable for such a critical item as CG.  Pilots don't like or trust automated features - at least not the pilots that live long enough to grow old.

@JonathanWalters, you are correct that it was actually a regional airline (out of PIA) under the Delta umbrella.

Here's an example of counterweights where every gram mattered, and the counterweights were still a sizeable fraction of the entire vehicle's mass.
On 2021 Feb 18, a few minutes before becoming an airplane,
the Martian probe Perseverance ejected 140 kg of tungsten
to move its center of mass off axis.
This changed its angle of attack from 0° to 16°, so its roll thrusters could steer it by banking.
A few minutes later it ejected about another 150 kg
to reduce its AoA to less than 5° before deploying its parachute, to dampen oscillations.
The same scheme worked in 2012 to land Curiosity.


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What are the differences between an EASA part-66 license and FAA A&P Aircraft Mechanic License?
what is the difference between EASA part-66 license and FAA A&P Aircraft Mechanic License? Are there any reasons for a company or individual to opt for the one or the other or both?

In the US (FAA) the aviation acronym AME stands for Aviation Medical Examiner. Instead, I think you must mean Aircraft Mechanic, A&P Mechanic, Aviation Maintenance Technician, or some equivalent.

Generally if you are regulated by EASA (Europe) you require part 66 engineers, if you are regulated by the FAA (USA) you require approved A&Ps. It's not really a case of a company having a choice. The individual would choose the path that is relevant to where they want to work.


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Is it possible to get a medical certificate from Canada and a pilot license in America?
I posted a question prior to this but it was too long and confusing. I have done some research and so I will ask:
If I obtain a medical certificate from Transport Canada (TC), and get my commercial pilot license through the FAA, can I work in the US as a commercial airline pilot and take school there?
I am a diabetic, so I can't obtain a class one or two medical certificate in America, but I can in Canada.
You can still fly in US airspace if you get a medical certificate from Canada, but I don't know if that's like from Canada into America.
Feel free to edit this question so it's more clear, I will include requirements from TC and such below.
On the second link, can someone explain it a little more to me? I am not great with understanding such things, I am sorry!
TC medical certificate regulations
Pilot medical certificate international use

Perhaps flying Canadian registered aircraft with a Canadian license, operating in US.  I knew a similarly situated pilot who worked for a Canadian survey company in the US.  Something about NAFTA.

(This is similar to this question - and see this answer in particular - but there may be some points here that deserve a separate answer.)
First, can you use a Canadian medical instead of a US medical, with a US pilot's certificate? The answer is no, with one (?) exception. If it were possible, then people could shop around other countries to find the easiest medical for them, which would be a huge loophole and would allow them to simply ignore the FAA's medical requirements. As a general statement, the country of your pilot's certificate and medical certificate must be the same.
The only exception I'm aware of is when you hold a foreign license and medical, and then ask the FAA to issue a foreign-based private certificate under 14 CFR 61.75. See this question for more information but basically, you would have to hold a Canadian pilot's license and medical first, and even then you would be limited by the privileges of the Canadian license.
Second, could you get a US commercial certificate using a Canadian medical? Yes, but only in a very roundabout way, and even then you couldn't use it. You'd first have to get an FAA foreign-based private certificate as I described above - which means getting a Canadian license first - and that certificate would be fine to use for a US commercial checkride. However, after passing the checkride you'd still need an FAA second-class medical to actually exercise your new commercial privileges.
Finally, another option would be to get a Canadian commercial license and medical, and then fly only Canadian aircraft in the US. I have no idea how practical that is because most countries don't allow cabotage, but maybe there's some way to make it work.
AFAIK diabetes is only disqualifying if you're insulin-dependent; if you're on oral meds you may still be able to get a Special Issuance for it. If you have any doubts about your personal situation then I'd suggest consulting an AME and/or calling AOPA, if you're a member.

Current special issuance for diabetes is discussed in my answer here: https://aviation.stackexchange.com/questions/341/can-a-person-with-type-1-diabetes-get-a-medical-and-learn-to-fly/79077#79077

You must hold an FAA first/second class medical certificate to be paid to fly In the USA. But  as a type one diabetic you can get a third class medical and are allowed to be a flight instructor (and obtain faa certificates) and all privileges that go along with being a third class medical holder.  You can also get a Canadian first class and second class medical and fly for Canadian carriers into USA. Per Chicago agreement (I think that’s what it’s called).

This looks like an answer, except for the last part which seems to form a separate question. Please note that answers on Stack Exchange are expected to be specifically answers to the question as asked. If you have a new question, use the "ask question" action link near the top of the page to ask it properly. Include a link to this or other questions if you feel that doing so provides context for your question. For the time being, I have proposed an edit to remove the question at the end.


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Is it "cutting off" in the pattern when I go before a plane that is going faster than I am but let me in first?
While turning from the 45˚ to the downwind leg for a downwind pattern landing in a Cessna 182, a Cheyenne was calling 5 miles out on a GPS approach for a straight in landing.  Clear day, both flying VFR, uncontrolled airport.  He and I had been communicating for 5-6 minutes, and I called my base turn knowing I had entered the pattern well ahead of him and had time to land ahead of him.  The Cheyenne pilot acknowledged me and was good with this.
Seconds before I touched down, I heard from a pilot evidently taxiing to take off from the same runway, "Dude ... you just cut off that Cheyenne ... you realize he's going about 4 times faster than you."
Now aside from his ignorance by not hearing the leadup conversation to our opposite direction approaches, when is a plane in a straight-on landing considered to have the right of way over one "in the pattern" and when, apart from communicating between pilots, is it proper regulation to land ahead, vs. extending the downwind leg and falling in behind him?
I was specifically trained that until you are within 4 miles, you are technically not on "final" during a straight-in approach ... but that common sense must prevail, so even if you reach the pattern first, it may be courteous and safer to allow a faster aircraft in ahead of you.

Assuming you were doing 50 knots in your Cessna 182, the Cheyenne would have been 200 knots on final......nope, I think that guy's accusation is unfounded.

The Cheyenne would have been "cutting you off", if he hadn't worked it out with the aircraft in the pattern and maintained visual separation.
According to the AIM, 4-3-3, standard pattern entry at an uncontrolled airport is abeam the midpoint in the downwind.

Enter pattern in level flight, abeam the midpoint of the runway, at pattern altitude. (1,000’ AGL is recommended pattern altitude unless established otherwise. . .)

http://www.faraim.org/aim/aim-4-03-14-189.html

Which was, naturally, my thinking, but I'm always more than happy to extend my downwind (if it's questionable) to a faster aircraft.  It's a tad bit upsetting to hear someone indict you on the CTAF like they were dubbed the local aviation police.

Sounds like nobody was even close to being in danger, so why get upset.

Since you and the Cheyenne pilot had it worked out you are ok and you made a proper entrance to the pattern. However its worth mentioning that there is at least one right of way rule that could apply here (depending on the situation).

Sec. 91.113
(g) Landing. Aircraft, while on final approach to land or while
  landing, have the right-of-way over other aircraft in flight or
  operating on the surface, except that they shall not take advantage of
  this rule to force an aircraft off the runway surface which has
  already landed and is attempting to make way for an aircraft on final
  approach. When two or more aircraft are approaching an airport for the
  purpose of landing, the aircraft at the lower altitude has the
  right-of-way, but it shall not take advantage of this rule to cut in
  front of another which is on final approach to land or to overtake
  that aircraft.

If the situation were that the Cheyenne was at say 2,000 ft on his final approach (even 5 miles out) and you overflew the field at 2,500 and made a teardrop entrance to the 45 descending 1000ft. in the process (putting you at 1,500ft. (lets call this pattern altitude)). You would in turn potentially be in breach of 91.113 since you cut in beneath him.
However in this brief on un-towered operations the FAA states that it is common courtesy to extend your downwind leg in this situation

Courtesy Tip
If another aircraft is on a straight-in instrument
  approach in visual conditions and it will not greatly inconvenience
  you, consider extending your downwind and announce your intentions.

With that in mind, there is no hard rule about it so you are in the clear, the extension is a courtesy to the other aircraft and intended mostly for safety reasons.
On a slight tangent, at a towered airport its likely your downwind leg would have been extended by the controller (which is where the courtesy tip most likely stems from) to allow the Cheyenne to come in. If the guy on the ground flys out of towered fields a lot he may be accustom to this style of operations and assumed a rule was broken. This happened to me while on my downwind at a towered airport, a little beech jet entered on the ILS and my downwind was extended to allow him in. That plane was so fast he was on the ground and at the FBO before I turned base.

You were not cutting off, since the other pilot let you in line ahead of him.
However, I'm a lazy pilot.   I'd have overwhelmingly decided to decline the offered cut-in and extend my downwind.  Having to hustle off the runway knowing there is a fast walker behind me is needless extra work and wear on the airplane.  I may have even extended further to let a plane holding short get off ahead of me.  My dad, an Alaska bush pilot, always said "you save so much time flying, there's no need to hurry."


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What are these symbols in Garmin Pilot?
When I start editing a flight plan in Garmin Pilot, if I have a distance that is farther (like 1,000 nm or farther) I get these two symbols in the map on the Flight Plan pane:

One is a tower and the other is an oval.
Here is the entire pane view:

Any idea what these two symbols are?
The tower looks like the same symbols as 'obstruction' from the Garmin Pilot manual, but note that the filed altitude is 39,000 feet (ie, no obstacles that high around here.)
What about the little oval?

I initially thought is was an indicator for 'midway fuel' but changing the initial fuel amount does not move the two symbols...

The first one is a lighted obstacle that is not a factor due to altitude, I think the second one is sky conditions but still trying to verify.

The first one is a lighted obstacle -- I don't think so. 1) It moves as the flight direction changes; 2) The flight plan is 39,000 feet so every lighted tower is irrelevant. I think the second one is sky conditions - Again, I don't think so. The tower and the oval, if present, are always the same distance apart and always right on the rhumb line

Is this Garmin Pilot for Android or iOS?

It is iOS. On the new iPad Pro

If you lower the altitude to something where you would have obstacles, does that change to some number?

It appears regardless of altitude.

Those are the highest obstacle and highest terrain point along the route, respectively. They're both grey because they're well below your planned altitude, so they're no factor.
You can see them by going to "Flight Plan", "Details", "Highest Point".

Great! It took me a while to find Highest Point. On my version, Press Flight Plan; Then press the blue ⓘ; The Highest Point for the details and Lat / Lon. Makes sense (obviously) that it is always on the rhumb line.

@dawg I'm on Android, so I'm not surprised it's a bit different!


text:
Is it possible to control the direction during auto-rotation?
Is it possible to control the direction during auto-rotation, and how does it work?

If you forget the fact that you are only ever going to go down (ignoring that in some types you might be able to go up for a short time) many helicopters are delightful to fly in autorotation.  You can fly forwards, descend straight down (0 kts) or even fly backwards - although most pilots find the latter really uncomfortable.

It's entirely possible.
Attitude control works the same way during autorotation as it does during normal powered flight. It's a good thing, too... during an autorotation you want to target your descent toward a suitable landing spot :-)
To (say) roll right, moving the cyclic causes the swashplate to move in such a way that the rotor blade's pitch (angle of attack) is greater during the left-side portion of the blade's travel, and lower during the right-side portion. This produces more lift on the left side, which causes a right-rolling moment on the helicopter.
The fact that the collective is all the way down and that the rotor's RPM is being maintained by airflow through the rotor does not change the way the cyclic produces attitude changes.
The anti-torque pedals still work too, although during an autorotation the pilot will promptly apply full right pedal, since lowering the collective will essentially eliminate torque from the rotor. Pedals can still be used for yaw though, as the tail rotor is still spinning (it is linked to the main rotor).
The "180° turning autorotation" is a common maneuver taught in basic training, where the pilot must set up the autorotative descent and then complete a 180° turn toward a landing spot.
For more information about autorotations in general, I recommend the FAA's (free online) Helicopter Flying Handbook. See page 2-24 for a general description, and page 11-2 for procedures/technique.
There are also lots of autorotation demonstration videos on YouTube that show maneuvering to a landing spot / 180° turns during the auto.

Thanks, that sounds pretty exciting, especially the part about the tail rotor. Now, i'm asking myself, what would happen if i had no tail-rotor (i.e. i'm sitting in a gyrocopter), would i start to spin?

@Hannes: Gyrocopter, better known as autogyro, always autorotates. It has normal rudder for directional control, which is sufficient, since autorotation produces very little torque.

@JanHudec; I think "better known as" might depend a little bit on where you are. If I'm not mistaken, they're usually indeed called "gyrocopters" over here. Cool point about them always auto-rotating, never thought of it that way.

@falstro: The wikipedia page is titled Autogyro and mentions autorotation as defining feature in the first sentence.

the pilot will promptly apply full right pedal, depends of course on which way the top is spinning.  You've assumed counter-clockwise.  Doing that in a clockwise spinner will result in an underwear changing "unusual attitude".


text:
What is the purpose of the three cylinders under the engines of the Junkers 52?
They're mounted underneath each engines on the JU-52. I saw them up close at the museum. Each one consists of bundled half-inch pipes running through the whole length, open at both ends.

The three cylinders hanging below each engine are the oil coolers - this page has a much closer shot which I've reproduced below.

Oil enters and exits the cooler through the two vertical lines and swirls around the hollow air channels. The cold air in flight moving through the tubes cools the oil, which is then returned to the engine.
Courtesy of eBay, here's a photo of an old, rusted-out cooler where you can clearly see the air channel tubes inside. (Using an oil cooler in this condition would promptly empty the engine of oil...)

Why is the oil cooled separately from the engine blocks? The Townend rings around the engine focus the airflow around the blocks - that's where the oil cooling should take place, it seems.

@SebastianHenckel On most air-cooled aircraft engines you'll find some kind of oil cooler assembly. While we call these engines "air-cooled" that's really only true of the cylinders and cylinder heads: the rest of the engine is really liquid (oil) cooled. Splash lubrication draws heat off the pistons into the oil, and the oil cooler dumps that heat to the outside air.


text:
What is the difference between a leading edge flap and a slat?
I always thought that the definition of slat was:
"Lift modifying and adjustable wing element on the leading edge of main airfoil."
and the definition of flap was:
"Lift modifying and adustable wing element on the trailing edge of main airfoil."
However, there are also leading edge flaps, also known as Krueger flaps, and they are located on the leading edge.
What gives these elements the name of "flap"? What is the main difference to slats?

"Krueger flaps are lift enhancement devices that may be fitted to the leading edge of an aircraft wing. Unlike slats or drooped leading edges, the main wing upper surface and its nose is not changed." Source: Wikipedia

related: http://aviation.stackexchange.com/q/1734/69

Slats are leading edge devices on aircraft that enable higher angles of attack. Flaps are devices on the leading (Krueger) and trailing edge which increase camber and the depth of the wing. Slats create a "slat" between the slat body and the wing leading edge so the air can pass from the bottom to the surface to hold off a stall to a higher AoA, flaps merely extend it fore and aft and direct the flow downwards for more lift. Both are mainly used in the low-speed situations of take-off and landing.

Does Krueger flap increase the stall angle of attack like as slat? Or it just increase the lift coefficient?

First of all, slats produce a slot (not slat) somewhat aft of the leading edge in order to allow high-speed air from below the wing to pass through and maintain laminar flow to a somewhat higher angle of attack.  They are a low-speed device.
There are also mid-wing slats which both produce drag and decrease lift and are used to slow down and get down, and, used on one wing at a time, cause roll.  They may be used at high speeds.
Both trailing edge flaps and LEDs (leading edge devices, be they leading edge Kreuger flaps or slats) increase camber in order to allow the wing to produce the same amount of lift at a lower airspeed (takeoff and landing).  They do not increase lift; if they did the aircraft would go up (and slow down rapidly) which is not the point.

Trailing edge flaps do increase lift at constant speed and AoA.

Not all leading edge flaps are Kreuger flaps, which rotate out from the lower forward wing surface. There are simple hinged leading edge flaps, as well. The example with which I am most familiar is the Chance-Vought F-8 Crusader. The entire leading edge droops simultaneous with trailing edge flap extension -- the inner wing section 25 degrees, the outer section 27 degrees on all US models except the F-8J. Lower stall speed and carrier approach speed are the reward. ref: F-8H NATOPS Manual.

That's not a flap, that's a droop.